The present invention relates to an improved aqueous ink for ink-jet printing.
Conventionally, to aqueous ink for fountain pens and pen recorders, and to stamping ink, there is added as a humectant a polyhydric alcohol, such as ethylene glycol, diethylene glycol, polyethylene glycol or glycerin, in order to prevent hardening of the ink at the tips of the pens and on the stamp pads.
In the case where ink containing one of the abovementioned polyhydric alcohols is employed for ink-jet printing, the polyhydric alcohol serves to prevent the ink from becoming hard within the nozzles of an ink-jet printing apparatus during the periods when the apparatus is not in use. However, in the case where the same ink supply is to remain in the printing apparatus for a long period of time, and the printing apparatus is used intermittently, for instance, once a week, and the periods of use and non-use are repeated, it frequently occurs that the dyes and other materials are separated from the ink in the form of precipitates and become affixed around the nozzles, so that the nozzles become plugged. As a result, it becomes difficult or totally impossible to eject the ink droplets from the nozzles as desired.
The above described problems of the conventional aqueous inks can be solved to some extent by increasing the amount of the polyhydric alcohols to be added to the inks. However, as the amount of the polyhydric alcohols in the ink increases (for instance, to more than 30 wt.%), the drying speed of the ink droplets deposited by printing on a recording sheet significantly decreases.